Digital packet-based networks, like the Internet, are increasingly being used to transmit voice signals. Given the asynchronous nature of packet-based networks, any extra complexity or delay in the network can present problems when the voice signal is reconstructed from its packetized form at the receiving end.
Voice-over-Internet-Protocol (VoIP) technology attempts to provide for voice communication over the Internet through the use of various communications protocols by which the voice signals can be encoded for transmission and decoded when received. In some cases, participants in a conversation will be using different protocols. Accordingly, it is necessary to convert a VoIP signal encoded in one protocol to a VoIP signal encoded using another protocol.
In a multi-speaker environment, the ability to mix signals from various participants in a mixer is important to providing a Quality of Service (QoS) comparable with traditional dedicated public-switched telephone network (PSTN) teleconferencing. Again, if participants are using different codecs, then the mixer must accommodate these differences and consolidate the signals into one mixed signal using a selected communications protocol.
Typical VoIP communications protocols include narrowband protocols G.711, G.729, and G.729(A), and wideband protocols 722 and 722.2.
The various communications protocols are typically applied to signals using codecs (encoders/decoders). Codecs are signal processing devices, usually implemented on a digital signal processor. They typically operate on a frame by frame basis, often with a buffer of frames for ‘lookahead’ purposes and/or to reduce jitter. This tends to introduce delay and complexity such that, in a mixer, the process of decoding a signal, mixing it with another signal, and encoding the mixed signal can result in problems, including packet loss, jitter, and end-to-end delay. All of these problems lead to difficulties in obtaining satisfactory QoS for VoIP.
Accordingly, there remains a need for VoIP technology having an improved QoS through reduced complexity and delay in transcoding and mixing.